Conventionally, silica sand has been widely used as molding sand. Because the silica sand is a mineral product, it is amorphous in its form, less in fluidity, and poor in filling ability. Therefore, the surface of a mold made of silica sand is rough, which therefore results in a rough surface of cast products (castings) and heavy load on the polishing step, a post-treatment step. In addition, quartz as a mineral component of the silica sand transforms its crystal structure to cristobalite or the like by thermal load during the casting, and degraded due to its volume change at this time, so that the silica sand is low in its regeneration efficiency. As a means for solving these problems, spherical molding sand (see, for example, JP-A-Hei-4-367349) and high silica-based spherical molding sand and a process for producing the same (see, for example, JP-A-Hei-5-169184) are disclosed. These molding sands are those prepared by forming raw material compositions into a spherical form by granulation, and thereafter baking in a rotary kiln or the like. However, the resultant molding sands are so low in spherical degree that fluidity and filling ability are insufficient and an effect of improving roughness of the surface of castings is small. Moreover, due to production by sintering method, only porous substances, in which many open pores are present and the water absorption is large, are obtained. Consequently, the strength of molds is insufficient, or a large amount of binder is required to produce molds, which makes the regeneration of molding sand difficult.